Active Countersound System with Special Arrangement of the Secondary Actuators for Reducing the Passage of Sound at an Open Boundary Area of Two Volumes; Active Countersound Arrangement; Method for Actively Reducing Sound

ABSTRACT

An active countersound system for actively reducing the sound waves of primary sound waves, with a regulator unit, an error sensor, a reference sensor and several secondary actuators. The secondary actuators are designed to emit countersound waves, wherein the regulator unit, which is coupled to the secondary actuators, processes an error signal and a reference signal, and generates a secondary signal, which by way of the coupling is conveyed to the secondary actuators in order to control the secondary actuators by means of the secondary signal such that said secondary actuators generate countersound waves that reduce the error signal so that optimal sound wave abatement is implemented, wherein the secondary actuators are arranged such that they are located on the margin of an open passage area, which passage area comprises a margin and is to be penetrated by the primary sound waves, in order to ensure active sound wave abatement of the open space that in the direction of passage is arranged behind the open passage area, of the countersound waves in the manner of a curtain.

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of German PatentApplication No. 10 2005 016 021.2 filed Apr. 7, 2005 and of U.S.Provisional Patent Application No. 60/669,061 filed Apr. 7, 2005, thedisclosure of which applications is hereby incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to an active countersound system for activelyreducing sound waves of at least one primary sound wave emanating from aprimary actuator that emits primary sound waves, with a specialarrangement of secondary actuators to reduce sound wave passage at orthrough an open boundary area of two volumes. Moreover, the inventionrelates to an active countersound system arrangement, a method foractively reducing sound waves, and the use of an active countersoundwave system for actively reducing sound waves for a control volume thatis at least partly open.

TECHNOLOGICAL BACKGROUND

Sound waves, in particular interfering sound waves such as noise, may bereduced either passively with noise-absorbing devices, or actively bymeans of active noise control (ANC) as it is generally known.

A known ANC system in principle functions as follows:

A primary actuator, such as for example a noise source, generates atleast one primary sound wave such as for example a sinusoidal soundwave. In order to actively reduce or even eliminate this interferingprimary sound wave, this primary sound wave has to be superimposed by asecondary sound wave or countersound wave of at best the same amplitudeand frequency but phase-shifted by 180°. To this effect an ANC regulatoris provided. This regulator processes a reference signal that issynchronous in relation to the primary sound wave, which referencesignal is for example acquired by means of a reference sensor, and anerror signal that has been recorded by an error sensor, for example byan error microphone, and from this calculates a secondary signal withthe frequency of the reference signal but with a different amplitude andphase. This secondary signal is conveyed to secondary actuators, forexample loudspeakers, which convert the secondary signal to acountersound wave or countersound waves. The superimposed waves are thenagain acquired by the error sensor, and regulating or controlling iscontinued so as to achieve minimisation of the resulting sound wave.

It is known for example—as stated in the report “Current and FutureIndustrial Applications of Active Noise Control” on the occasion ofACTIVE 04 in Williamsburg, Va. of 20-22 Sep. 2004 by Colin H Hansen,Active Noise and Vibration Control Group, School of MechanicalEngineering, University of Adelaide, SA 5005, Australia,chansen@mecheng.adelaide.edu.au—by means of an ANC system to abate orreduce sound waves in a tube, i.e. a semi-open control volume with twoopen passage areas. However, this is a simple overall system withone-dimensional sound wave propagation, in which system active soundwave reduction can easily be implemented by arranging a secondaryactuator within the tube.

Furthermore, it is known to implement active sound wave reduction inclosed control volumes.

From the report “Active Sound Control on the Flight Deck of a C130Hercules”—also presented within the framework of ACTIVE 04 inWilliamsburg, Va. from 20-22 Sep. 2004 by Jon Gorman, Richard Hinchliffeand Ian Stothers, Ultra Electronics Controls Division, Vitrum Building,St. John's Innovation Park, Cowley Road, Cambridge, CB4 0WS, England,jon.Gorman@ultracontrols.aero—an ANC system has been disclosed whichwithin a closed control volume, namely in an aircraft fuselage,attenuates local areas, or reduces the primary sound wave in localareas.

The report “An actively controlled triple-glazed window” presented at“The 33rd International Congress and Exposition on Noise ControlEngineering” (inter-noise 2004) from 22-25 Aug. 2004 in Prague, CzechRepublic, by A. Jakob, R. Bauers, M. Möser, Institute of TechnicalAcoustics, Technical University of Berlin, Einsteinufer 25, D-10587Berlin, Germany, andrejakob@tu-berlin.de discloses an ANC system for atriple-glazed window. Here, too, in a closed control volume in a voidbetween two glass panes of the triple glazing, active sound wavereduction of primary sound waves is effected. In this arrangement thesecondary actuators are arranged at the margin of the interspace thuscausing a reduction of the sound waves in the interior of the closedcontrol volume. In this way the passage of sound through the closedwindow into the volume behind may be reduced.

The above illustrated systems are associated with a disadvantage in thatactive sound wave reduction is possible either only in closed controlvolumes or in simple geometric control volumes with one-dimensionalsound wave propagation in the interior of the control volumes.

SUMMARY OF THE INVENTION

Amongst other things, it may be an object of the present invention toimplement effective active sound wave reduction of primary sound wavesthat propagate in several directions in a control volume or space thatis at least partly open, wherein sound wave reduction takes place notonly locally but in relation to the entire space or the entire controlvolume.

This object may be met by an active countersound system with a specialarrangement of secondary actuators for reducing the passage of sound atan open boundary area of two volumes with the characteristics accordingto the independent claim 1; moreover the object of the present inventionmay be met by an active countersound system arrangement, a method foractively reducing sound waves, and the use of an active countersoundsystem for actively reducing sound waves for a control volume that is atleast partly open, with the characteristics according to the remainingindependent claims.

The active countersound system according to the invention comprises atleast one regulator unit, at least one error sensor, at least onereference sensor and one or several secondary actuators. The secondaryactuators are designed to emit countersound waves. The error sensor,which is coupled to the regulator unit, acquires the superimposed soundwaves and, if they are acquirable, conveys them as an error signal tothe regulator unit by way of the coupling. The reference sensor, whichis coupled to the regulator unit, acquires the primary sound wave, ofwhich there is at least one, and conveys a corresponding referencesignal to the regulator unit by way of the coupling. The regulator unit,which is coupled to the secondary actuators, processes the error signaland the reference signal and from them generates a secondary signal thatis conveyed to the secondary actuators by way of the coupling so as tocontrol the secondary actuators by means of the secondary signal,dependent on the error signal, such that said secondary actuatorsgenerate countersound waves that reduce the error signal so that optimumsound wave abatement may be achieved.

In this setup the secondary actuators are arranged such that they arelocated on the margin of a passage area that is at least partly open,which passage area comprises a margin and is to be penetrated by theprimary sound waves, in order to ensure active sound wave abatement ofat least part of the space arranged behind the passage area, which spaceis at least partly open, of the countersound waves in the manner of acurtain.

Furthermore, according to the invention an active countersoundarrangement with a control volume and with an active countersound systemwith the above-described characteristics is created for activelyreducing sound waves of the primary sound waves in the control volume.

In the method according to the invention for active abatement of soundwaves of at least one primary sound wave emanating from a primaryactuator that emits primary sound waves, by means of a reference sensora reference signal of a primary sound wave is acquired. Furthermore, bymeans of an error sensor an error signal is acquired by superimposedsound waves. By means of couplings the error signal and the referencesignal are transmitted to a regulator unit. Furthermore, the regulatorunit evaluates the transmitted signals, and a secondary signal isgenerated. The secondary signal is transmitted by means of coupling tosecondary actuators. The secondary actuators are arranged on the marginof an open passage area for the primary sound waves. Furthermore, bymeans of the secondary actuators, secondary waves are generated from thetransmitted secondary signal, which secondary waves in the manner of acurtain are superimposed on the open passage area so that the primarysound wave that propagates through the open passage area is at leastreduced and/or eliminated, wherein the steps are repeated and/orcontinuously carried out in the active countersound system that isdesigned as a control circuit.

Furthermore, according to the invention the use of an activecountersound system for actively reducing sound waves in an at leastpartly open control volume is provided.

A fundamental idea of the invention comprises the fitting of an activecountersound system with secondary actuators, wherein the secondaryactuators are arranged such that they are arranged so as to be marginal,i.e. along the margin of an open passage area for primary sound waves,and so that they generate secondary sound waves or countersound wavesthat in the open passage area are superimposed on the primary soundwaves, thus reducing or eliminating the primary sound waves. In this waya kind of “acoustic curtain” may be created through which all primarysound waves in their direction of propagation behind the passage areamay at least be reduced.

Generally speaking, primary waves are noise waves. Accordingly,secondary waves or countersound waves are corresponding (phase-shifted)noise waves. Correspondingly, secondary actuators for generating thesenoise waves are loudspeakers.

An open passage area is an area surrounded by a closed margin, throughwhich area the primary sound wave(s) reache(s) the space or the controlvolume.

The margin can have any closed geometric shape. In particular, however,the margin may be arranged in one plane. For example, the margin can bedesigned as a circumference of a simple geometric figure comprisingtriangles, circles, ovals, ellipses, quadrangles, polygons, squares,rectangles, trapeziums, lozenge shapes or the like.

The margin can also be designed as a so-called envelope so thatencapsulation of a primary actuator that is designed as a noise sourcecan be achieved. In this way the entire surroundings behind thisenvelope would undergo primary sound wave reduction.

The secondary actuators are preferably arranged so as to be equidistantalong the margin of the passage area. In this way, optimum primary soundwave reduction can be achieved. Equidistant distribution along themargin makes it possible to design simpler computing models with simpleralgorithms for regulating or controlling the active countersound system,thus ensuring more effective primary sound wave reduction.

The number of secondary actuators for effective primary sound wavereduction depends on a multitude of parameters comprising the geometryof the space to be shielded, or on the control volume, geometry of thepassage area, spectral composition of the primary sound wave(s),amplitude and/or frequency of the primary sound wave(s), bandwidth ofthe primary sound wave(s), degree of the desired sound wave reductionand the like.

The term “space to be shielded” refers to the space or the controlvolume in which active (primary) sound wave reduction is to take place.

Generally speaking, the denser the countersound wave curtain and thebetter, i.e. among other things the faster and more accurate, theregulator unit, the higher the primary sound wave reduction. This meansthat in order to achieve effective primary sound wave reduction,corresponding quality and/or quantity of the secondary actuators andcorresponding quality of the regulator unit or, generally speaking, ofregulation, should be ensured.

In the case of a narrow-band primary sound wave only narrow-bandsecondary actuators are necessary. In the case of primary sound waveswith a large amplitude, for example more powerful secondary actuators ora correspondingly greater number of secondary actuators are necessary.Due to the host of possible applications it is however not possible tostate all the option of the various designs, depending on thecombination of parameters.

The same applies to the type of secondary actuators. Here, too, foreffective reduction of primary sound waves the type of secondaryactuators depends on many parameters comprising the geometry of thespace to be shielded or the control volume, geometry of the passagearea, spectral composition of the primary sound wave(s), amplitudeand/or frequency of the primary sound wave(s), bandwidth of the primarysound wave(s), degree of the desired sound wave reduction and the like.

Analogous to the above example of a primary sound wave of largeamplitude, either a larger number of secondary actuators or the samenumber of secondary actuators with means to generate a countersound wavealso of larger amplitude may be required. If the frequency of theprimary sound wave is in a low frequency range, only secondary actuatorsto generate a low frequency range may be necessary.

Also on the basis of the correlation of the parameters among each other,it is not possible in the present document to list all the combinationsand/or embodiments. However, in particular some combinations, forexample a large number of high-quality secondary actuators and fasthigh-quality regulation, result in effective primary sound wavereduction, wherein the design size, in particular of the secondaryactuators, also always should be taken into account.

In addition, the position of the error sensors may have an influence onthe effectiveness of the active countersound system.

Just like the type and number of secondary actuators, the number and/ortype of error sensors also depends on parameters such as the geometry ofthe space to be shielded, the control volume, geometry of the passagearea, spectral composition of the primary sound wave(s), amplitudeand/or frequency of the primary sound wave(s), degree of the desiredsound wave abatement and the like.

Furthermore, the reference sensor and the error sensor may be designedso as to be integrated in one sensor. In this way both so-calledfeedforward systems and feedback systems can be designed. Thus from areference signal that is otherwise obtained by means of a referencesensor, said reference signal can also be obtained from the errorsensors and reference sensors that have been combined and integrated inone sensor.

The use of the active countersound system according to the invention,with the special marginal arrangement of the secondary actuators foractively reducing sound waves for an at least partly open controlvolume, is manifold. For example, the active countersound system can bearranged in entrance regions of noise-attenuated spaces in order toachieve effective noise reduction. In particular primary actuatorsdesigned as noise sources can effectively be encapsulated with thissystem. Similarly, for example in workshop halls, certain areas, inwhich for example due to legal requirements noise reduction ismandatory, can be effectively protected against the effects of noise,without the need to meet noise protection measures for the entireworkshop hall.

This results in a multitude of application options of activecountersound arrangements with an at least partly open control volume,with an open passage area with a margin, and with an active countersoundsystem according to the invention.

For example, with the arrangement of secondary actuators along a planerectangle with several of these arrangements, individual regions canquasi be designed in the manner of an acoustic partition or barrier as anoise-attenuated zone. Also imaginable are embodiments on airfields,along highways or railway lines, construction sites and the like.

The use of the arrangement according to the invention is associated withan advantage in that said arrangement does not visually block out theopen passage area, as is for example the case in passive noiseprotection barriers. The use as a noise protection barrier or noiseprotection barrier element may also provide an advantage in thatessentially only the acoustic perception is altered.

Preferably, the arrangement of the secondary actuators or of the marginof the open passage area is designed as a simple geometric figure. Inthis way several of these arrangements can be arranged together in amodular way, also in order to generate large-area noise protection.

When compared to the ANC system relating to a triple-glazed window, asstated above, the system proposed in the present invention is effectivealso with the window open. In this application the use or the functionas an “acoustic curtain” becomes particularly clear.

SHORT DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the invention is shown in the FIGURE and isexplained in more detail below.

The FIGURE shows an in-principle diagram of an active countersoundsystem according to the invention.

The illustrations in the FIGURE are diagrammatic and not to scale.DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Below, with reference to the figure, an active countersound systemarrangement 30 according to one embodiment of the invention isdescribed.

The active countersound system arrangement 30 comprises an activecountersound system 10 and a control volume 20. The active countersoundsystem 10 comprises a regulator unit 11, two error sensors 12, areference sensor 13 and four secondary actuators 14. The secondaryactuators 14 are designed as loudspeakers with which countersound waves15 can be generated. These countersound waves 15 are sinusoidal soundwaves and are acquired by means of the two error sensors 12, which inthe present embodiment are correspondingly designed as microphones. Theerror sensors 12 are coupled to the regulator unit 11 by means of lines.By way of this line the error signal F acquired by the error sensors 12is transmitted to the regulator unit 11. A primary sound wave 16,generated by a primary actuator (not shown) is acquired by the referencesensor 13 as a reference signal R. In this embodiment the primary soundwave 16 is shown in the shape of a sinusoidal noise wave or sound wave.Correspondingly, in this embodiment the reference sensor 13 is amicrophone. The reference sensor is also coupled to the regulator unit11 by way of a coupling designed as a line. By way of this line thereference signal R is transmitted to the regulator unit 11. Theregulator unit 11 evaluates the two transmitted signals R, F and fromthem calculates a secondary signal S. The regulator unit 11 is coupledto the secondary actuators 14 by way of lines. By way of this couplingthe secondary signal S generated by the regulator unit is transmittedfrom the regulator unit 11 to the secondary actuators 14.Correspondingly, the secondary actuators 14 convert the secondary signalS to countersound waves 15 onto which the primary sound wave 16 issuperimposed. This superimposed sound wave or these superimposed soundwaves is/are again acquired by the error sensors 12, and regulating iscontinuously carried out or repeated.

The control volume 20 is designed as a partly open control volume, whichin the figure is diagrammatically illustrated as a right parallelepipedwhose one side is designed as an open passage area 21. Through this openpassage area 21 the primary sound wave 16, or the primary sound wave 16′or sound waves onto which the countersound wave(s) has/have beensuperimposed, or which primary sound wave 16′ has been attenuated by thecountersound wave(s), reaches/reach the interior of the control volume20.

The open passage area 21 is surrounded by a margin. Along this margin,which in the embodiment shown is rectangular in shape, the secondaryactuators 14 are arranged. In this arrangement the secondary actuators14 are spaced apart from each other so as to be equidistant. Thecountersound waves 15 emitted by the secondary actuators 14 along theopen passage area 21 form a type of “acoustic curtain” so that noprimary sound wave 16 can pass the open passage area 21 towards theinterior of the control volume 20 without these countersound waves 15being superimposed on it. The superimposition generates an attenuatedprimary sound wave 16′, wherein the degree of attenuation is to beequated with the reduction in noise or reduction in the primary soundwave.

In addition it should be pointed out that “comprising” does not excludeother elements or steps, and “a” or “one” does not exclude a pluralnumber. Furthermore, it should be pointed out that characteristics orsteps which have been described with reference to one of the aboveembodiments can also be used in combination with other characteristicsor steps of other embodiments described above. Reference characters inthe claims are not to be interpreted as limitations.

REFERENCE LIST

-   10 Active countersound system-   11 Regulator unit-   12 Error sensor-   13 Reference sensor-   14 Secondary actuator-   15 Countersound wave-   16 Primary sound wave-   16′ Superimposed/attenuated primary sound wave-   20 Control volume-   21 Open passage area-   F Error signal-   R Reference signal-   S Secondary signal

1. An active countersound system for actively reducing the sound wavesof at least one primary sound wave emanating from a primary actuatorthat emits primary sound waves, with at least one regulator unit; withat least one error sensor; with at least one reference sensor; withseveral secondary actuators; wherein the secondary actuators aredesigned to emit countersound waves; wherein the error sensor, which iscoupled to the regulator unit, acquires the superimposed sound waves,which are conveyed as an error signal to the regulator unit by way ofthe coupling; wherein the reference sensor, which is coupled to theregulator unit, acquires the primary sound wave, of which there is atleast one, which is conveyed to the regulator unit by way of thecoupling; wherein the reference sensor and the error sensor are designedso as to be integrated in one sensor; wherein the regulator unit, whichis coupled to the secondary actuators, processes the error signal andthe reference signal, and generates a secondary signal, which isconveyed to the secondary actuators by way of the coupling in order tocontrol the secondary actuators, depending on the error signal, by meansof the secondary signal such that said secondary actuators generatecountersound waves that reduce the error signal so that optimum soundwave abatement is implemented; wherein the secondary actuators arearranged such that they are located on the margin of a passage area thatis at least partly open, which passage area comprises a margin and is tobe penetrated by the primary sound waves, in order to ensure activesound wave abatement of at least part of the space arranged behind theopen passage area, which space is at least partly open, of thecountersound waves in the manner of a curtain.
 2. The activecountersound system of claim 1, in which the secondary actuators areequidistant along the margin of the open passage area.
 3. The activecountersound system of claim 1, in which the number of secondaryactuators has been selected depending on parameters such as the geometryof the space to be shielded, geometry of the open passage areas,spectral composition of the primary sound wave(s), amplitude and/orfrequency of the primary sound wave(s), degree of the desired sound waveabatement.
 4. The active countersound system claim 1, in which the typeof secondary actuators has been selected depending on parameters such asthe geometry of the space to be shielded, geometry of the open passagearea, spectral composition of the primary sound wave(s), amplitudeand/or frequency of the primary sound wave(s), degree of the desiredsound wave abatement.
 5. The active countersound system claim 1, inwhich several error sensors are in place, wherein the number and/or thepositioning of the error sensors have/has been selected depending onparameters such as the geometry of the space to be shielded, geometry ofthe open passage area, spectral composition of the primary soundwave(s), amplitude and/or frequency of the primary sound wave(s), degreeof the desired sound wave abatement.
 6. A method for actively abatingsound waves of at least one primary sound wave emanating from a primaryactuator that emits primary sound waves, in which method by means of areference sensor a reference signal of a primary sound wave is acquired;by means of an error sensor an error signal of superimposed sound wavesis acquired; wherein the reference sensor and the error sensor aredesigned so as to be integrated in one sensor; by means of couplings theerror signal and the reference signal are transmitted to a regulatorunit; the regulator unit evaluates the transmitted signals, and asecondary signal is generated; the secondary signal is transmitted bymeans of coupling to secondary actuators; the secondary actuators arearranged on the margin of an open passage area for the primary soundwaves; and the secondary actuators from the transmitted secondary signalgenerate countersound waves which in the manner of a curtain aresuperimposed on the open passage area so that the primary sound wavethat propagates through the open passage area is reduced or eliminated,wherein the steps are carried out repeatedly in a control circuit.
 7. Anactive countersound system arrangement, comprising an at least partlyopen control volume with an open passage area with a margin; comprisingan active countersound system of claim 1 for actively reducing the soundwaves of the primary sound waves in the control volume.
 8. The use of anactive countersound system for actively reducing sound waves for acontrol volume that is at least partly open.
 9. An active countersoundsystem arrangement, comprising an at least partly open control volumewith an open passage area with a margin; comprising an activecountersound system of claim 2 for actively reducing the sound waves ofthe primary sound waves in the control volume.
 10. An activecountersound system arrangement, comprising an at least partly opencontrol volume with an open passage area with a margin; comprising anactive countersound system of claim 3 for actively reducing the soundwaves of the primary sound waves in the control volume.
 11. An activecountersound system arrangement, comprising an at least partly opencontrol volume with an open passage area with a margin; comprising anactive countersound system of claim 4 for actively reducing the soundwaves of the primary sound waves in the control volume.
 12. An activecountersound system arrangement, comprising an at least partly opencontrol volume with an open passage area with a margin; comprising anactive countersound system of claim 5 for actively reducing the soundwaves of the primary sound waves in the control volume.